Micro-electromechanical systems (MEMS) are very small devices manufactured using a variety of lithography based process for controlling the deposition and removal of material layers on a substrate. One early example of a MEMS device, described in U.S. Pat. No. 3,614,677, is the resonistor—an electromechanical monolithic resonator. There are many applications of MEMS, broadly categorized as sensors, actuators and structures. One type of actuator includes ink jet actuators.
A useful structure in some MEMS devices is a diaphragm. For example, in a microphone or acoustic sensor, a diaphragm can be made that will resonate and couple its energy well to the acoustic field in the environment. A simple process for making a diaphragm involves depositing a layer of the diaphragm material onto a silicon substrate and then removing a portion of the substrate through an etching process, leaving the diaphragm material suspended over the resulting cavity. Typically, such diaphragm material has a high tensile strength, so it is not very flexible or stretchy. An enhancement in performance and flexibility of the diaphragm can be achieved by providing the diaphragm with a corrugated shape. Scheeper et al. describe one way to produce a corrugated microphone diaphragm (Journal of Micro-electromechanical Systems Vol. 3, No. 1, March 994, pages 36-42).
Fluidic MEMS devices, such as an ink jet print head, often feature fluid filled chambers that are in fluidic communication to allow a fluid to move through the device. It is well understood in the art that such chambers can be made by using a mask material layer, typically a photoresist layer, that can then be selectively exposed using an optical mask with a pattern of transparent and opaque regions that will then allow an actinic light to selectively expose only certain regions of the mask layer. This causes a reaction that will either harden the exposed region (in the case of a positive photoresist) or the unexposed region (with a negative photoresist). Subsequent etching will then remove the mask layer in select regions thereby forming the chambers. The chambers are finished by filling with a sacrificial material and then depositing a roof layer followed by removal of the sacrificial material.
One type of ink jet print head is based on the thermal ink jet (TIJ) or bubble jet technology. Typical thermal ink jet inks are aqueous based fluids. A resistive heater embedded in the wall of a fluid chamber is energized to boil the ink in the fluid chamber. A vapor bubble forms over the heater to force fluid out a nozzle and eject a drop. Thermal ink jet technology is typically used in home/office printers due to its low cost and high resolution although it has been used in some industrial and commercial printing applications. However, its use in these types of applications is considered to be limited due to narrow ink latitude (need to boil ink to form bubbles) and short print head life (corrosive ink attack hot heaters). The print speed of existing thermal inkjet technology is also often too slow due to low drop generation frequency.
Another type of ink jet print head is based on piezoelectric ink jet (PIJ) technology. A piezoelectric actuator forms part of the wall of a fluid chamber. When the piezoelectric actuator is energized, the deformation or displacement of the actuator causes the pressure in the fluid chamber to rise to force fluid out a nozzle and eject a drop. Piezoelectric ink jet technology is widely used in industrial printing due to its wide ink latitude and long print head life. However, the piezoelectric ink jet print head has low nozzle density and high manufacturing cost comparing to thermal ink jet print head due to small actuator displacement. As a result, the piezoelectric print heads are usually large in size and expensive to make. The print speed of existing piezoelectric ink jet technology is also often too slow due to low drop generation frequency.
Therefore, there is an ongoing need for an ink jet print head that is low cost and has high resolution, wide ink latitude, and long print head life.